Scientists invent a paper battery – just add water

Discarded electronics are accumulating rapidly, prompting researchers to explore creative ways to reduce the resulting waste, known as electronic waste. Now a team has made a disposable water-activated battery made of paper and other sustainable materials.

The cables, screens and batteries that make up our devices, not to mention the plastic, metal and other materials that enclose them, are filling landfills with dangerous debris. Some e-waste is relatively large – old cell phones, air conditioners, and radios, to name just a few common items. Other e-waste is more insidious, such as single-use electronic medical diagnostic kits, environmental sensors, and smart labels that contain disposable batteries and other equipment.

“It’s these little batteries that are a big deal,” says Dele Ogunseitan, a professor of public health at the University of California, Irvine, and a green technology researcher and consultant for major technology companies, who was not involved in the paper battery development. “Nobody really pays attention to where they end up.”

Researchers from the Cellulose & Wood Materials Laboratory at the Swiss Federal Laboratories for Materials Science and Technology (EMPA) are working to address this overlooked problem. This week they published an article in Scientific reports describing a new water activated paper battery that they developed with environmentally friendly materials. Such a device could possibly present a sustainable alternative to the more damaging batteries that are common in low-power devices.

The new paper battery has the same key components as standard batteries but packs them differently. Like a typical chemical battery, it has a positively charged side called the cathode, a negatively charged side called the anode, and a conductive material called an electrolyte between the two. The components of a traditional battery are enclosed in plastic and metal; in the new battery, the anode and cathode are inks printed on the front and back of a sheet of paper. That paper is infused with salt, which dissolves when the paper is moistened with water. The resulting salt water solution acts as an electrolyte.

Sustainable materials were a prerequisite for the researchers, who considered only non-toxic and abundant ingredients to create their device. “We were pretty confident that we would have something that would work in the end, but the development of these ink materials and systems is anything but trivial,” says Gustav Nyström, head of the Cellulose and Wood Materials Laboratory and senior author of the study. . After trying hundreds of formulations for the different components, the scientists opted for graphite ink to make the cathode, zinc ink for the anode, and salt-infused paper to make the electrolyte. When the paper is dry, the battery is stable. Add just a couple of drops of water, however, and the built-in salt dissolves, allowing the electrons to flow. After the paper has been moistened, the battery takes approximately 20 seconds to activate. At that point, it produces a stable 1.2 volts of electricity until the paper dries. (For comparison, an AA battery delivers 1.5 volts.) When the researchers rewetted the paper, the battery produced 0.5 volts for more than an hour.

Although researchers have shown that their battery could power an alarm clock, disposable paper batteries are unlikely to replace the standard AAs on store shelves. Instead Nyström envisions a future where these batteries are integrated into diagnostic tests and environmental sensors, ideally with other sustainable components such as screens and packaging. That future may not be that far off.

It is difficult to predict a timeline for producing such items on a large scale, but Nyström says he is in contact with potential industry partners and believes these batteries could make their way into products within the next two to five years. “The performance you see on this device, I think, is already sufficient for many of these applications,” he says. It is mainly about increasing production and integrating batteries into systems such as diagnostic tests and environmental sensors.

Basically, Nyström says his team created the battery without compromising sustainability criteria. “This is work that really starts with developing sustainable materials,” she explains. From there, she says, “I think we’ve been able to create something that’s quite useful.”

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